What’s the Difference Between a Floatplane and a Seaplane?

A well-known TV business commentator and Aviation Analyst recently asked me “What is the difference between a floatplane and a seaplane.” On a newscast he called a floatplane a seaplane and the know-it-all’s bombarded him with comments telling him he got it wrong. Well this know-it-all (me) will explain the difference and prove that the Aviation Analyst was correct.

Let’s start with the technical definitions bearing in mind that the dictionaries often get this wrong to start with. To fully understand the difference, however, we also have to add both Flying Boats and Amphibians to the mix.

My Definitions:

Floatplane: A fixed-wing airplane with one or two pontoons (together known as floats) fixed as undercarriage used for taking off and landing (or alighting) on water. The pontoon design, much the same as a speed boat, has a water tight planing hull capable of creating buoyancy (displacement) when resting on water and hydrodynamic lift when taking off and landing (alighting) on water. Floats without gear are called straight floats. There are many examples such as the Cessna C206, C208, Norseman, Beaver, Otter, Beech 18 and even the Viking Twin Otter.

DHC-6 300 Series Viking Twin Otter “floatplane” on straight floats.

DHC-6 400 Series Viking Twin Otter “floatplane” on straight floats.

Wipline 8750 pontoons being paired to make up a set of floats for the C208 Caravan

Cessna C206 “floatplane” on straight floats.

Turbine DHC-3 Otter “floatplane” on straight floats.

DHC-2 Beaver “floatplane” on straight floats.

Flying Boat: A fixed-wing airplane with the fuselage built into the shape of a water proof hull capable of creating buoyancy when resting on water and hydrodynamic lift when taking off and landing (alighting) on water. A flying boat always remains capable of landing on water but can be configured with landing gear as amphibious to also land on the land. Examples of amphibian flying boats are the Grumman Goose, Grumman Mallard, PBY Catalina Canso, Lake Buccaneer and Dornier Seastar. The Spruce Goose and the Boeing 314 (Pam Am Clipper) were straight flying boats and had no landing gear.

The Martin M-130 is the airliner that gave Pan Am the true ability to span the world’s oceans. Often called a “China Clipper” after the most famous of the three M-130’s built for Pan American, this aircraft introduced the modern era of long-distance international air travel. The M-130 provided scheduled commercial passenger service across the Pacific ocean from 1935 through World War II.

Amphibian: A fixed-wing airplane that can takeoff and land on both land and water. An amphibian airplane can be a floatplane or flying boat outfitted with retractable gear designed to extend for runway landings and retract for water landings. For example the Viking Twin Otter and the Cessna C208B EX can be configured for landplane only, floatplane only, or amphibian floatplane by installing the Wipline 13000 and the Wipline 8750 floats respectively.

C208B EX being converted from landplane to amphibious floatplane version at Wipaire facility.

C208 675 converted from land plane version to amphibious floatplane version at Wipaire facility.

So what is the main difference between a flying boat and a floatplane?

A floatplane can have the pontoons (the floats) removed and replaced with fixed landing gear where afterwards the airplane can only takeoff or land on land. A flying boat cannot be reconfigured as a land plane only.

C208 Landplane version on the left and floatplane on the right.

OK so what then is a seaplane? That is where the definition gets trickier.

Seaplane: By the general definition – which proves the TV Aviation Analyst correct – a seaplane is any fixed-wing aircraft that can takeoff and land on water. The definition for a Seaplane is basically the same definition as the French Hydravion. You can safely call a Catalina, Beaver, Cessna 185, Cessna 206, Twin Otter, Grumman Goose, Grumman Mallard, Cessna Caravan, Dornier Seastar, Quest Kodiak or a Douglas DC-3 a seaplane as long as it can (and is designed to) takeoff and land on water. The US Airways Airbus A320 making a water landing on the Hudson River does not count as a seaplane because it wasn’t designed to do so and because well… it could not take off again.

By my definition, however, there is a distinction that goes beyond the technical configuration of a regular floatplane or flying boat. A seaplane also has to operate on the sea.

According to international law all the ocean is a sea but the overall definition of the term sea, however, not only defines a large body of salty water, such as the Philippines Sea, but it also describes the surface condition of the sea or what we call the sea state.

In oceanography, a sea state is the general condition of the free surface on a large body of water—with respect to wind waves and swell—at a certain location and moment. A sea state is characterized by statistics, including the wave height, period, and power spectrum. The sea states vary with time, as the wind conditions or swell conditions change. The sea state can either be assessed by an experienced observer, like a trained mariner, or through instruments like weather buoys, wave radar or remote sensing satellites.

We call any flying off the ocean open water experience. In other words, bodies of water where the sea state can can get pretty rough depending on the wind strength, wind duration (length of time the wind is blowing on the water surface), fetch (distance the wind has to blow over the water surface), natural barriers such as reefs, islands, sand bars, breakwaters, or peninsulas (the ability to stop swells and waves from building) and the presence of ocean borne swells (areas open to the sea without any protective barrier).

The further from a protective barrier and the longer the fetch the more open the area will be. Ocean swells, formed by storms, typhoons, and hurricanes, can travel thousands of kilometers from their point of origin making open water areas difficult to assess for water landings without actually being there. One day it can be relatively calm and two days later swells as high as a horse can crash down on a shoreline, beach or barrier reef.

The islands around Seattle, Vancouver Island, West Coast Inner Passage and most of Alaska are not really considered open water because you can land the seaplane in the seaport’s protected inner waters. It’s still the sea but the many islands and peninsulas protect the landing areas from the open ocean swells. Fiji, Indonesia, the Maldives and the Philippines are truly open water seaplane areas because none of the protective reefs, islands and lagoons are exclusive. The strong winds, long fetches and breaks (gaps) in the protective reefs and islands allow big swells to power up and power in.

Landing on a rough day in open water is called landing in big water. Big can mean when the seaplane is in the trough the pilot cannot see over the top of the next swell. Taking off in rough water and large swells is called a green water takeoff because often the spray created from submarining through the swells while trying to get airborne can splash such large sheets of water on the windshield that the water appears green. That is a lot of water. It’s like throwing a wash tub of water on your windshield.

Just a few months ago I witnessed a seaplane landing in 2 meter high swells. During the touch down the seaplane launched airborne off the first swell and then nose-dived through the second swell disappearing in the blue water and ensuing spray. The seaplane literally submerged out of sight for a few seconds only to bob up again at a complete standstill with the engine still running. It was a testimony to the strength of the seaplane but not necessarily a testimony to the superior skill of the pilot. For sure it wasn’t a testimony of the superior judgement of the pilot. I had just landed in the same area but behind a protective breakwater only a few minutes away where the water was flat calm.

So the critical factor in deciding whether a floatplane can be used as a seaplane and whether a floatplane pilot can fly as a seaplane pilot is whether or not the seaplane can survive open sea operations and whether or not a floatplane pilot has the experience and knowledge to handle rough water landings or green water takeoffs. Once the floatplane pilot gains the experience and skills to fly in the open sea he graduates or transcends to the status of a seaplane pilot. The only exception is Captain Chesley B. “Sully” Sullenbery who we shall award the Honorary Degree of Seaplane Captain for executing a perfect seaplane landing on the Hudson River with his Airbus A320. Now someone just needs to teach Sully how to takeoff again using a real seaplane.

So if someone asks you what is the difference between a floatplane and a seaplane you can either say “all floatplanes can be seaplanes but not all seaplanes are floatplanes.” Or you can simply say “seaplanes land and takeoff on the sea.”

If someone asks you what is the difference between a floatplane pilot and a seaplane pilot you can say “all seaplane pilots can be floatplane pilots but not all floatplane pilots are seaplane pilots.” Or you can simply say “seaplane pilots land and takeoff on the sea.”

Three M-130’s were built: NC-14714 – Hawaiian Clipper NC-14715 – Philippine Clipper NC-14716 – China Clipper All three M-130’s were lost in accidents: The Hawaiian Clipper disappeared east of Manila under mysterious circumstances in July, 1938; the Philippine Clipper was flown into a mountain north of San Francisco in bad weather on January 21, 1943, killing its crew and a group of Navy officers including the Pacific submarine chief, Rear Admiral R.R. English; and the China Clipper itself sank at Port of Spain, Trinidad, on January 8, 1945.